U.S. patent number 5,237,227 [Application Number 07/874,677] was granted by the patent office on 1993-08-17 for exciter rotor flow through cooling.
Invention is credited to John B. Huss.
United States Patent |
5,237,227 |
Huss |
August 17, 1993 |
Exciter rotor flow through cooling
Abstract
An electrical power generating system (10) for generating
alternating current in accordance with the invention includes a
main generator (14) for generating the alternating current having a
stator (22) and a rotor (24) and an excitor (12) for generating
excitation current of the main generator having a stator (16) and a
rotor (18) With the rotors being coaxial and driven by an input
shaft (36); a cylindrical non-electrically conductive containment
sleeve (70) mounted in surface contact with the coaxial rotors so
that the rotors fit within the sleeve to provide support for the
rotors against centrifugal acceleration and for containing coolant
liquid inside the cylinder and an outside surface facing an inner
cylindrical surface of the stator; and a coolant circuit (50) for
circulating the coolant liquid to cool windings (30) of the main
generator rotor and windings (42) of the excitor rotor, the coolant
circuit including a first portion (52) through which flows the
coolant liquid received from a coolant input (50) through the
windings of the main generator rotor and a second portion (56)
through which liquid coolant flows into contact with the windings
of the excitor rotor with the containment sleeve preventing coolant
from flowing radially outward into an air gap between the rotors
and stators of the main generator and the excitor.
Inventors: |
Huss; John B. (Rockton,
IL) |
Family
ID: |
25364316 |
Appl.
No.: |
07/874,677 |
Filed: |
April 27, 1992 |
Current U.S.
Class: |
310/54;
310/68D |
Current CPC
Class: |
H02K
9/197 (20130101); H02K 19/38 (20130101); H02K
11/042 (20130101) |
Current International
Class: |
H02K
19/16 (20060101); H02K 9/19 (20060101); H02K
11/04 (20060101); H02K 19/38 (20060101); H02K
9/197 (20060101); H02K 009/00 (); H02K
011/00 () |
Field of
Search: |
;310/54,59,61,62,68D,68R,89,112,262,43,44,165 |
References Cited
[Referenced By]
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77236 |
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356830 |
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439474 |
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450287 |
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165046 |
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290043 |
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GB |
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Primary Examiner: Stephan; Steven L.
Assistant Examiner: To; E.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus
Claims
I claim:
1. An electrical power generating system for generating alternating
current comprising:
a main generator for generating the alternating current having a
stator and a rotor and an exciter for generating excitation current
for the main generator having a stator and a rotor with the rotors
being coaxial and driven together by an input shaft;
a cylindrical non-electrically conductive containment sleeve
mounted in surface contact with the coaxial rotors so that the
rotors fit within the sleeve for providing support for the rotors
against centrifugal acceleration and for containing coolant liquid
inside the sleeve and having an outside surface facing an inner
cylindrical surface of the stators; and
a coolant circuit for circulating the coolant liquid to cool
windings of the main generator rotor and windings of the exciter
rotor, the coolant circuit including a first portion through which
flows the liquid coolant received from a coolant input through the
windings of the main generator rotor and a second portion through
which liquid coolant flows to immerse the windings of the exciter
rotor with the containment sleeve preventing coolant from flowing
radially outward into an air gap between the rotor and stator of
the main generator and the exciter.
2. An electrical power generator in accordance with claim 1 further
comprising:
a rectifier assembly for rectifying alternating current produced by
the exciter with the rectified alternating current exciting the
windings of the rotor of the main generator disposed axially
between the coolant input and the main generator rotor with liquid
coolant flowing from the coolant input through the rectifier
assembly prior to flow to the first and second portions of the
coolant circuit.
3. An electrical power generator in accordance with claim 1 further
comprising:
an end cap connected to an end of the containment sleeve and
extending radially inward into contact with an end piece which
extends radially outward from the coolant input; and
a port within the end cap which extends through the end cap at a
location radially inward from the containment sleeve for draining
coolant liquid from the second portion of the coolant circuit in
which windings of the exciter rotor are immersed into a sump.
4. An electrical power generator in accordance with claim 2 further
comprising:
an end cap connected to an end of the containment sleeve and
extending radially inward into contact with an end piece which
extends radially outward from the coolant input; and
a port within the end cap which extends through the end cap at a
location radially inward from the containment sleeve for draining
coolant liquid from the second portion of the coolant circuit in
which windings of the exciter rotor are immersed into a sump.
5. An electrical power generator in accordance with claim 3
wherein:
the end piece includes a shaft to which the rotors are attached to
which the end cap is connected; and
the sleeve, end cap and the shaft define a chamber which is part of
the second portion of the coolant circuit in which windings of the
exciter rotor are immersed.
6. An electrical power generator in accordance with claim 4
wherein:
the end piece includes a shaft to which the rotors are attached to
which the end cap is connected;
the sleeve and the shaft define a chamber which is part of the
second portion of the coolant circuit in which windings of the
exciter rotor are disposed; and
the rectifier assembly is disposed inside the shaft.
7. An electrical power generator in accordance with claim 6 further
comprising:
a passage in the second portion of coolant circuit extending
through the shaft to permit liquid coolant to flow radially outward
from the rectifier assembly into the chamber defined by the sleeve,
end cap and shaft.
8. An electrical power generator in accordance with claim 7 further
comprising:
a rectifier housing containing the rectifier assembly with a
channel cut in an outside wall of the housing which is part of the
second portion of the coolant circuit which couples liquid coolant
flowing through the rectifier assembly to the passage.
9. An electrical power generator in accordance with claim 1 wherein
the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
10. An electrical power generator in accordance with claim 2
wherein the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
11. An electrical power generator in accordance with claim 3
wherein the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
12. An electrical power generator in accordance with claim 4
wherein the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
13. An electrical power generator in accordance with claim 5
wherein the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
14. An electrical power generator in accordance with claim 6
wherein the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
15. An electrical power generator in accordance with claim 7
wherein the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
16. An electrical power generator in accordance with claim 8
wherein the nonconductive sleeve comprises:
a thermoset resin and graphite fiber.
Description
TECHNICAL FIELD
The present invention relates to cooling systems for excitor
generators in electrical power generating systems having a main
generator which is excited by an excitor.
BACKGROUND ART
The Assignee of the present invention manufactures self-excited
electrical power generators for use in airframes which utilize a
permanent magnet generator for generating a field for an excitor
generator which generates alternating current which is rectified by
a diode assembly to produce the field for the main generator. Oil
is utilized as a cooling medium which is circulated through the
diode assembly of the generating system for rectifying the
alternating current produced by the excitor generator and through
the rotor of the main generator for dissipating heat. The oil
cooling permits the diode assembly and windings of the rotor of the
main generator to be driven with higher currents which permit
higher outputs. The leakage of oil into the air gap between the
stator of the main generator and the rotor of the main generator
creates windage losses.
Examples of fluid cooled electric generators are disclosed in U. S.
Pat. Nos. 2,894,155, 2,897,383, 3,439,201, 3,469,127, 4,647,805 and
4,728,840. None of these systems utilizes a sleeve for containing
coolant fluid from migrating radially outward from a rotor to the
air gap between the rotor and the stator. As a result, leakage of
coolant fluid can cause reduced efficiency especially in view of
the natural propensity of oil which is the typical coolant used in
cooling generators to leak from a coolant flow path.
U. S. patent application Ser. No. 765,017, entitled "Structurally
Tailored Non-Metallic Stator Cooling Fluid Containment Sleeve"
filed on Sep. 24, 1991, which is assigned to the Assignee of the
present invention, discloses a sleeve which is press fit into the
annulus of a stator which is formed from a plurality of
laminations. The sleeve performs numerous functions including the
containing of oil from flowing from the windings of the stator into
the air gap between the stator and the rotor. As a result, the
sleeve provides effective oil containment to prevent leakage of oil
into the air gap between the inner diameter of the sleeve and the
outer diameter of the rotor of the electric machine.
Electrical power generators which are manufactured by the Assignee
for use in airframes have utilized spray cooling of oil of the
excitor rotor. Spray cooling of the rotor of the excitor creates
leakage of the oil into the air gap between the rotor and the
stator of the excitor which reduces efficiency as a consequence of
windage losses. Moreover, spray cooling does not immerse the
windings of the rotor of the excitor in oil which reduces the
overall efficiency of cooling over that which would be realized if
a mechanism existed for containing the windings of the excitor
rotor immersed in oil.
DISCLOSURE OF INVENTION
The present invention is an improved oil cooled generator of the
type utilized in airframes which includes an excitor and a main
generator which are coaxially mounted and cooled by a single
coolant circuit for circulating the coolant fluid to cool windings
of the main generator rotor and windings of the excitor rotor. With
the invention, a cylindrical non-electrically conductive
containment sleeve is press fit in surface contact with the coaxial
rotors so that the rotors fit within the sleeve and are supported
to provide hoop strength against rotational stresses produced by
the high rates of revolution of the rotors which are used in
alternating current electrical power generators in airframes. The
excitor rotor oil, which flows in the coolant circuit that cools
windings of the main generator rotor and windings of the excitor
rotor, is contained radially inward of the air gap to reduce
windage losses when compared to windage losses caused by spray
cooling of the rotor windings of the excitor rotor in the prior
art. While the containment sleeve results in increased spacing
between the field windings and the main windings of the excitor,
the increased cooling provided to the excitor permits higher
current densities to be utilized so that the size of the excitor
generator is not increased. As a result, the overall efficiency of
the electrical power generating system is increased by reducing
windage losses by containment of oil radially inward from the air
gap between the stator and rotor. Moreover, the containment sleeve
and an end cap produce a pool of coolant liquid in which the
windings of the excitor generator are immersed to produce enhanced
cooling when compared to that produced in the prior art by spraying
coolant liquid on the rotor windings of the excitor generator.
An electrical power generating system for generating alternating
current in accordance with the invention includes a main generator
for generating the alternating current having a stator and a rotor
and an excitor for generating excitation current for the main
generator having a stator and a rotor with the rotors being coaxial
and driven together by an input shaft; a cylindrical
non-electrically conductive containment sleeve mounted in surface
contact with the coaxial rotors so that the rotors fit within the
sleeve for providing support for the rotors against centrifugal
acceleration and for containing coolant liquid inside the sleeve
and having an outside surface facing an inner cylindrical surface
of the stators; and a coolant circuit for circulating the coolant
liquid to cool windings of the main generator rotor and windings of
the excitor rotor, the coolant circuit including a first portion
through which flows the liquid coolant received from a coolant
input through the windings of the main generator and a second
portion through which liquid coolant flows to immerse the windings
of the excitor rotor with the containment sleeve preventing coolant
from flowing radially outward into the air gap between the rotor
and the stator of the main generator and the excitor. The invention
further includes a rectifier assembly for rectifying alternating
current produced by the excitor with the rectified alternating
current exciting the windings of the rotor of the main generator
disposed axially between the coolant input and the main generator
rotor with liquid coolant flowing from the coolant input through
the rectifier assembly prior to flow to the first and second
portions of the coolant circuit. The invention further comprises an
end cap connected to an end of the containment sleeve and extending
radially inward into contact with an end piece which extends
radially outward from the coolant input; and a port within the end
cap which extends through the end cap at a location radially inward
from the containment sleeve for draining liquid coolant from the
second portion of the coolant circuit in which windings of the
excitor rotor are immersed into a sump. The end piece includes a
shaft to which the rotors are attached to which the end cap is
connected; and the sleeve, end cap and shaft define a chamber which
is part of the second portion of the coolant circuit in which
windings of the excitor are immersed. The rectifier assembly is
disposed inside the shaft. The invention further comprises a
passage in the second portion of the coolant circuit extending
through the shaft to permit liquid coolant to flow radially outward
from the rectifier assembly into the chamber defined by the sleeve,
end cap and shaft. The invention further includes a rectifier
housing containing the rectifier assembly with a channel cut in an
outside wall of the housing which is part of the second portion of
the coolant circuit which couples liquid coolant flowing through
the rectifier assembly to the passage. The nonconductive sleeve
comprises a thermoset resin and graphite fiber.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 illustrates a view of an electrical power generating system
for generating alternating current in accordance with the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 illustrates an electrical power generating system 10 for
generating alternating current in accordance with the present
invention. A preferred application of the electrical power
generating system 10 is in an airframe for the generation of 400
Hz. three-phase alternating current. The generating system 10 is
self-excited by a permanent magnet generator (not illustrated) for
exciting excitor generator 12 which provides excitation for main
generator 14. The excitor generator 12 is comprised of a stator 16
and a rotor 18 which is joined to shaft 20. The main generator 14
is comprised of a stator 22 and a rotor 24 which is joined to the
shaft 20. The shaft 20 is hollow and contains a rectifier assembly
26 which is contained in a housing 28. The rectifier assembly
comprises a three-phase fullwave rectifier assembly containing a
plurality of semiconductor diodes for rectifying the alternating
current produced by the excitor generator 12. The DC rectified
current produced by the rectifier assembly 26 is applied to the
field windings 30 of the rotor 24 of the main generator 14. The
alternating current produced by the generating system 10 is
produced by stator windings 32. As illustrated, the main generator
is a two-pole generator having pole pieces 34 which face into and
outside of the plane of FIG. 1. Torque for driving the coaxial
rotors which are attached to shaft 20 is applied to input 36. The
DC output from the rectifier assembly 26 is applied to terminals
which are electrically connected to terminal connectors 40 which
make electrical contact with the field windings 30 of the main
generator rotor 24. Three phase alternating current is produced by
the windings 42 of the excitor rotor 18. Terminals 44 which are
connected to the output of the windings 42 are connected to the
terminal connectors 46 which are electrically connected to the
input of the rectifier assembly 26. Fasteners 48 retain the pole
pieces 34 of the main generator rotor 24 in the shaft 20.
The assembly of the present invention described above is a known
assembly of a two-pole, three-phase alternating current
self-excited electrical power generator utilized in an
airframe.
The present invention contains a coolant circuit 50 for circulating
coolant liquid, which preferably is oil, to cool the field windings
30 of the main generator rotor 24, excitor windings 42 of the
excitor rotor 18 and the rectifier assembly 46. The coolant circuit
is comprised of a first portion 52 through which flows the coolant
liquid received from a coolant input 54 and a second portion 56
through which liquid coolant flows into contact with the windings
42 of the excitor rotor 18. The coolant circuit contains a third
portion 58 connected between the input 50 and an input to the first
portion 52 and a second portion 56 in which is disposed the
rectifier assembly 26. The first portion 52 receives liquid coolant
which has flowed through the rectifier assembly 26. The oil flowing
through the third portion 58 picks up heat generated by fullwave
rectification performed by the rectifier assembly of the
alternating current produced by the windings 42 of the excitor
generator rotor 18. The coolant liquid flows from the third portion
58 radially outward into the second portion 52 and axially along
the windings 30 which are wound around a magnetic circuit coupled
to the pole pieces 34. The liquid coolant flows axially along the
shaft 20 in contact with the windings 30 into output 62 from which
the coolant liquid flows. The second portion 56 also receives
liquid coolant flowing radially outward from the third portion
after passing through the rectifier assembly 26. A slot 64 cut in
the outside surface of the housing 28 of the rectifier assembly 26
receives coolant liquid flowing radially outward. The coolant
liquid flows along the slot 64 from left to right to passage 66.
The passage 66 connects a first part of the second portion 56 of
the coolant circuit 50 to a second part of the second portion. The
second part of the second portion 56 of the coolant circuit 50 is
disposed radially outward from the first part. The second part
contains a chamber 68 in which coolant liquid collects to immerse
the windings 42 of the exciter rotor 18. The immersion of the
windings 42 in a pool of coolant liquid in the chamber 68 provides
a higher degree of cooling than the spray cooling of the prior art.
A cylindrical non-electrically conductive containment sleeve 70 is
force fit over the outside surface of the rotors 18 and 24 to
provide reinforcing to increase the hoop strength of the rotor
assembly against centrifugal acceleration. The containment sleeve
70 forms the outside wall of the chamber 68 so that coolant liquid
is retained inside of the air gap between the stator 16 and rotor
18 of the exciter generator 12. End cap 72, which may be integral
with the sleeve 20 or attached thereto, extends from one end of the
sleeve 70 to the shaft 20 for forming a closure to prevent the
coolant liquid in which the windings 42 of the excitor rotor are
immersed from running axially outward to prevent the windings from
being immersed. Port 74, which is located radially inward from the
containment sleeve 70 in the end cap 72, drains coolant liquid from
the second portion 56 of the coolant circuit 50 in which the
windings 42 of the excitor rotor 18 are immersed. The coolant
draining from the port 74 runs into sump 76 and drains outward from
drain 78. The structure extending from the input 54 of the coolant
circuit 50 radially outward to the shaft 20 is an end piece.
Preferably, the rotor containment sleeve 70 is electrically
non-conductive and provides substantial hoop strength to resist
centrifugal acceleration of parts of the rotors radially outward
into the air gap which is disposed between a stator containment
sleeve 80 and the rotor containment sleeve 72 and also retains oil
from migrating radially outward into the air gap between the rotor
containment sleeve 70 and the stator containment sleeve 80. The
reason that the rotor containment sleeve 70 is preferably
non-conductive is that with a metallic containment sleeve eddy
currents will be induced in the portion of the sleeve which is
magnetically coupled to the sinusoidal varying magnetic field
produced by current flow in the windings 42 of the rotor 18 of the
excitor generator 12. Eddy currents reduce the overall efficiency
of the operation of the generating unit by dissipating energy
inputted by the input 36. Moreover, eddy currents result in heat
being generated within the rotor containment sleeve 70 which
further results in a requirement for additional cooling. Eddy
currents are produced by the time varying magnetic field produced
by the windings 42.
While the rotor containment sleeve 70 may be made by various
processes using resinous non-conductive materials, a preferred
composition of the rotor containment sleeve is a thermoset resin
containing graphite. The graphite functions to reinforce the
strength of the containment sleeve 70 which provides the hoop
strength required to resist centrifugal acceleration of the rotors
18 and 24. A graphite or graphite fiber reinforced cylindrical
sleeve, which is formed with a thermosetting resin, is light in
weight, high in strength and is heat resistant which is ideal for
the environment of an alternating current generator such as those
utilized in airframes. However, it should be understood that the
formulation of the cylindrical rotor containment sleeve is not
limited to the use of thermoset resins reinforced with graphite and
may be practiced with any non-electrically conductive composition
which provides sufficient hoop strength and oil containment.
While the invention has been described in terms of its preferred
embodiment, it should be understood that numerous modifications may
be made thereto without departing from the spirit and scope of the
invention as defined in the appended claims. It is intended that
all such modifications fall with the scope of the appended
claims.
* * * * *